Purkinjie image-based alignment of suction ring in ophthalmic applications

ABSTRACT

An alignment device including means for releasably attaching a suction ring and means for applying a pattern of light to an eye of a patient. The alignment device further including means for detecting light reflected from the eye and determining whether the suction ring is aligned relative to the eye based on the detected light.

This application claims the benefit of priority under 35 U.S.C. § 119(e)(1) of U.S. Provisional Application Ser. No. 61/300,125 titled Purkinjie Image-Based Alignment of Suction Ring in Ophthalmic Applications, filed Feb. 1, 2010, the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and system for aligning and attaching a suction ring to an eye of a patient during an ophthalmic application.

BACKGROUND

A well centered anterior capsulotomy is an important factor in obtaining an optimal refractive outcome in intraocular lens (IOL) implantation, particularly for accommodating or pseudo accommodating IOLs, IOLs used to correct spherical aberration, or toric IOLs. The reason for this is that surgeons use the position of the capsular opening as a visual landmark to center the IOL. The centration is important both optically and mechanically. Optically, if the IOL, center of curvature of the cornea and fovea are not in proper alignment, image quality suffers from aberrations and mechanically, if the IOL is not centered with respect to the lens capsule equator, the lens may, over time, tilt or become more easily displaced, leading to optical aberrations or necessity of a secondary procedure to explant or re-center the IOL.

Currently, the anterior capsular opening is torn manually using a procedure known as continuous curvilinear capsulorhexis (CCC). In the absence of any other visual landmark, the opening is centered as well as can be accomplished manually, using the dilated pupil as the reference. Since the pupil is known to, on the average, dilate significantly asymmetrically, the current procedure, if successfully accomplished, tends to leave the IOL systematically off center with respect to the line of sight and the optic axis of the eye.

Ideally, the IOL should be centered on the visual axis; however, this cannot be determined intraoperatively. An alternative placement which can be determined and which allows IOL placement close to the natural state is to center the IOL such that the optical axes of the IOL and cornea be collinear. If the anterior capsulotomy cut can be positioned concentrically around the optic axis of the cornea and crystalline lens, i.e. such that the optic axis of the eye is maintained after implantation, then an IOL implanted and centered on the capsular opening would be close to optimally positioned.

BRIEF SUMMARY

One aspect of the present invention regards an alignment device including means for releasably attaching a suction ring and means for applying a pattern of light to an eye of a patient. The alignment device further including means for detecting light reflected from the eye and determining whether the suction ring is aligned relative to the eye based on the detected light.

A second aspect of the present invention regards an alignment device that includes a housing having a mechanism that releasably engages a suction ring and a light source connected to multiple light emitters that are arranged in a pattern so that the light emitters apply light in the pattern of light to an eye of a patient. The device further includes a detector that detects light reflected from the eye and determines whether the suction ring is centered on the eye based on the detected light.

A third aspect of the present invention regards a method of aligning a suction ring on an eye, the method including positioning a suction ring over an eye of a patient and applying a pattern of light to the eye. The method further includes detecting light reflected from the eye and determining whether the suction ring is aligned relative to the eye based on the detected light.

One or more aspects of the present invention allow for improved visual outcomes of cataract surgery by allowing more accurate and stabile placement of an IOL to reduce optical aberrations of the eye.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitute part of this specification and, together with the general description given above and the detailed description given below, serve to explain features of the present invention. In the drawings:

FIG. 1 is an exploded view of an embodiment of an alignment device in accordance with the present invention;

FIG. 2A-I show various possible off-axis images formed by the alignment device of FIG. 1;

FIG. 3A shows a possible on-axis image formed by the alignment device of FIG. 1; and

FIGS. 3B-D show the individual images of the fourth, first and third Purkinjie images, respectively, formed by the alignment device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention regards a method and system for aligning and attaching a suction ring to an eye of a patient during an ophthalmic application that involves the use of a laser system. Examples of possible laser systems with which the present invention can be used are the laser systems described in U.S. patent application Ser. Nos. 11/337,127; 12/217,285; 12/217,295; 12/509,412; 12/509,021; 12/509,211 and 12/509,454, the entire contents of each of which are incorporated herein by reference.

Such laser systems may employ an associated disposable Patient Interface Device (PID) which is used to register and immobilize the patient's eye relative to the laser, allow efficient delivery of the treatment laser to the cornea and crystalline lens and allow images of the lasing process to be provided to the user to monitor progress in the procedure. Like other ophthalmic ultrashort pulse lasers used for cutting corneal or crystalline lens tissue, the PID has two parts: a suction ring which is applied manually to the patient's eye and a docking part which is attached to the laser and then guided, via a joystick-controlled 3-axis motion control system, to dock the laser with the suction ring on the eye.

In accordance with the present invention, a Purkinjie reflection-based alignment device 100 is used with a laser system, such as those described previously, which allows the suction ring 102 to be centered about the optic axis of the eye. As noted above, such a centration will allow optimal placement of the implanted IOL. As shown in FIG. 1, the device 100 includes a two part handle 102 that houses built in batteries 104 and a syringe 106 for applying vacuum to the suction ring 134. The batteries 104 power up a semi-circular light source that includes several light generators, such as LEDs (light emitting diodes) 112, that are activated when a switch (not shown) is turned on. Ideally, the LEDs 112 are infrared so that they cannot be seen by the patient but visible LEDs could also be used. A holder 114 for the LEDs 112 has a flange 120 with mounting holes 124 to hold the LEDs 112 in their correct positions, aimed through the center of a conical holding device 130 and suction ring 134 which is attached to the distal end of the conical holding device 130 at the beginning of the procedure. The conical holding device 134 has an upper edge 132 that is attached to the underside of the semi-circular housing 122 that holds the LEDs 112. A viewing device, such as a camera 128 or a viewing lens, can be used to view an image of the eye of the patient as will be described hereinafter. In the case of using a camera 128, the camera and its associated camera lens are mounted so that the camera lens axis is collinear with the axis defined by the center of the suction ring 134 and the center of the semi-circular ring of LEDs 122. The camera image of the eye as viewed through the opening 116 of the holder 114 and through the center of suction ring 134 is displayed on a separate monitor (not shown).

In use, the device is held by the handle 102 and is positioned over the eye as the surgeon watches the image of the eye on the monitor. The patient, if not subjected to a retrobulbar block or other means to immobilize the eye, would be instructed to stare straight ahead or at a distant fixation light (not shown in diagram) visually located within the open circle defined by the semi-circular Purkinjie light source but not connected to the device 100. This is to maintain the patient's fixation in a relatively constant direction so that the device 100 can be positioned properly relative to that fixation direction. If the LEDs 112 emit visible light, it is helpful to have the fixation light (not shown) be of a different color so that the patient can more easily stare at the fixation light without distraction from the LEDs 112.

When the device is close enough to the eye, Purkinjie reflections from the posterior lens surface (fourth Purkinjie image), anterior cornea surface (first Purkinjie image), and anterior crystalline lens surface (third Purkinjie image) will be formed and imaged on the monitor as shown in FIGS. 3B-D, respectively. When the suction ring 134 is perfectly aligned, that is, the camera axis is collinear with optic axis of the eye, the Purkinjie reflections corresponding to the first, third and fourth Purkinjie's images will appear simultaneously as shown in FIG. 3A. Each of the three Purkinjie reflections of FIGS. 3B-D appears as a semi-circle. The first Purkinjie reflection and the fourth reflection appear as semi-circular arrays of reflected LEDs “facing” each other; the opposite (convex rather than concave) curvature of the cornea compared to the posterior lens surface causes the inversion of one of the images such that it “faces” the other. The third Purkinjie image is oriented similarly to the first Purkinjie reflection since these two surfaces have the same direction of curvature. The sizes of the individual LED images in the various Purkinjie reflections as well as the different diameters of the semi-circles are functions of the geometry of the measurement angle, i.e. distances and angles between LEDs 112 and the various eye surfaces and the radii of curvature of the cornea, anterior lens surface and posterior lens surface. However the positions and orientations of the semi-circular reflections are what are of interest for the alignment, not the diameters of the semi-circles or the appearances of the individual LED reflections. To make clear how the Purkinjie reflections help the surgeon correctly align the suction ring to the eye, FIGS. 2A-I show the Purkinjie reflections when the eye is looking off to the left, right, up and down, relative to the axis of the suction ring. With experience, by looking at the orientation and position of the Purkinjie reflections shown on the camera monitor, the surgeon can adjust the position and angle of the handheld device 100 of FIG. 1 to properly align the suction ring 134 with the optical axis of the eye. When the Purkinje reflections of FIG. 3A are shown, it indicates that the optic axis of the suction ring 134 is collinear with the optic axis of the eye. When proper alignment is achieved, the suction ring 134 is pressed onto the eye by actuating a latch (not shown) outside the body of the handle 102 to allow a spring (not shown) to actuate a spring-loaded syringe 106. In particular, prior to actuating the latch, the syringe 106 is compressed (syringe plunger all the way in). Upon actuation of the latch the spring pushes the syringe plunger outward creating a vacuum inside the syringe 106 and, via a piece of tubing (not shown), in the suction ring 134. Creation of the vacuum in the suction ring 134 results in the clamping of the suction ring onto the eye. The handheld device 100 of FIG. 1 is then released from the suction ring 134 and removed. The release can be accomplished simply by pulling the handheld device 100 from the suction ring 134 which is now attached to the eye, if there is only a light friction fit between the suction ring 134 and the conical holding device 130. Alternatively, the conical holding device 130 could include a mechanism (not shown) which releasably engages the suction ring 134. A release lever (not shown) on the handle 102 could be in mechanical communication with the release mechanism so that when it is activated, the suction ring 134 is released.

Following the alignment and attachment of the suction ring to the eye, the surgeon moves the joystick to dock a locking snap ring at a distal end of the arm with the suction ring 134. When the locking ring and suction ring 134 are docked, they constitute in combination a patient interface device (PID). The PID registers and immobilizes the patient's eye during treatment with a laser and thus the PID allows for efficient delivery of the treatment laser to the cornea and crystalline lens and allows images of the lasing process to be provided to the user to monitor progress in the procedure. An example of the above described PID is disclosed in Applicants' provisional applications filed on Jan. 29 and Feb. 1, 2010 having attorney docket numbers 12212/66 and /69, respectively, and each having the title of “Servo Controlled Docking Force Device for Use in Ophthalmic Applications,” the entire contents of which are incorporated herein by reference.

Note that the application of a patient interface device with any form of planar or curved applanation perturbs the shape and axis of the cornea, thereby eliminating any possibility of determining the optic axis of the eye once the patient interface device is applied. Therefore if the suction ring 134 is to be applied such that it is centered on the optic axis, the determination of the optic axis must be made before applying the suction ring 134.

While the above described process regards device 100 being handheld, the Purkinjie-based device could also be built into the joystick controlled 3-axis of motion optical head of an ophthalmic laser. In this case, the image of the Purkinjie reflections would still be used to judge when the suction ring was centered, however, the patient's eye or head and optical head of the laser would need to be manipulated to get the best positioning of the suction ring on the eye.

Note that for cutting an anterior capsulotomy with a laser, the position of the crystalline lens capsule must be determined since the capsulotomy cut is made through the capsule. A Scheimpflug camera based measuring system could be used to make this determination. Optical coherence tomography or other methods could equally be used for the measurement. If the suction ring 134 is well centered on the optic axis, the apex of the crystalline lens, i.e. the point at highest elevation along the optic axis of the laser, will fall on the optic axis of the lens. The circular anterior capsulotomy can then be cut around the apex.

If the suction ring 134 is not centered, and assuming that the crystalline lens is, to a good approximation, spherical over the central region, the apex of the lens will not fall on the optic axis. In this latter case, there is no good way to determine where the anterior capsulotomy should be cut. If the circular cut is centered about the apex of the crystalline lens, which is tilted with respect to the axis of the laser, the cut will be centered off the optic axis of the eye and the IOL will be subsequently de-centered if it is, as is general practice, centered by reference to the capsulotomy.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims. 

1. An alignment device comprising: means for releasably attaching a suction ring; means for applying a pattern of light to an eye of a patient; and means for detecting light reflected from said eye and determining whether said suction ring is aligned relative to said eye based on said detected light.
 2. An alignment device comprising: a housing comprising a mechanism that releasably engages a suction ring; a light source connected to multiple light emitters that are arranged in a pattern so that the light emitters apply light in said pattern of light to an eye of a patient; and a detector that detects light reflected from said eye and determines whether said suction ring is centered on said eye based on said detected light.
 3. A method of aligning a suction ring on an eye, the method comprising: positioning a suction ring over an eye of a patient; applying a pattern of light to said eye; and detecting light reflected from said eye and determining whether said suction ring is aligned relative to said eye based on said detected light. 